VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-39377: Jupyterlab · nbconvert has an Arbitrary File Write via Path Traversal in Cell Attachment Filenames

Affects jupyterlabSource GCVE Database

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Authoritative record:CVE-2026-39377· Medium 6.5

Not known to be exploited · CVSS 6.5 Medium : upgrade to 4.5.6_3 when convenient.

Data as of 30 Oct 2026, 09:15 UTC

CVSS 3.1 base score

6.5Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 4.5.6_3

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade jupyterlab to 4.5.6_3.

Affected software

Product	Affected	Fixed in
Homebrewjupyterlab`pkg:brew/jupyterlab`Other threats	Affected >=3.4.3 <4.5.6_3	Fixed in 4.5.6_3

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade nbconvert to version 4.5.6_3 or later where the vulnerability is fixed. Alternatively, disable the ExtractAttachmentsPreprocessor by setting 'c.ExtractAttachmentsPreprocessor.enabled = False' in the nbconvert configuration to prevent processing of cell attachments and mitigate the risk.

Description

A path traversal vulnerability in Jupyterlab's nbconvert component (CVE-2026-39377) allows arbitrary file writes outside the intended output directory via crafted cell attachment filenames. The ExtractAttachmentsPreprocessor does not sanitize filenames, enabling attackers to control the destination path, filename, extension, and content of files written to the filesystem. This can lead to unauthorized file creation or modification with the privileges of the nbconvert process. The issue affects versions from 3.4.3 up to but not including 4.5.6_3. A fix is available in version 4.5.6_3, and disabling the ExtractAttachmentsPreprocessor is a recommended workaround.

Impact

An attacker can write arbitrary files with attacker-controlled content to any location accessible by the nbconvert process, potentially leading to unauthorized modification or creation of files on the host system. This could be leveraged to alter application behavior or inject malicious files, but the impact is limited by the permissions of the nbconvert process. There is no direct confidentiality or availability impact reported.

Summary

The nbconvert tool in Jupyterlab suffers from an arbitrary file write vulnerability due to insufficient sanitization of cell attachment filenames in the ExtractAttachmentsPreprocessor. This allows an attacker to perform path traversal attacks by embedding '../' sequences in attachment filenames, resulting in files being written to arbitrary locations on the filesystem. The attacker can fully control the file path, name, extension, and content, constrained only by the permissions of the nbconvert process. This vulnerability is tracked as CVE-2026-39377 and has a CVSS v3.1 score of 6.5 (medium severity). It affects nbconvert versions >=3.4.3 and <4.5.6_3. The issue is fixed in nbconvert 4.5.6_3. As a mitigation, the ExtractAttachmentsPreprocessor can be disabled to prevent exploitation.

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Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 09:15 UTC

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